Coating composition and method for the improvement of surface hardness of article by the use thereof

ABSTRACT

A coating composition comprising (A) partially hydrolyzed silicon compounds, (B) an acrylic copolymer and/or a polyol and optionally (C) an etherified methylolmelamine, which is useful for improving the surface properties, such as surface hardness and chemical resistance, of plastics products, wooden products, metallic products, etc. by coating the products therewith, said products being optionally previously under-coated with an under coating composition comprising a copolymer of vinyl monomers and optionally other copolymerizable monomer(s), by which the adhesion between the coating film and the base material is improved to give a formed article having excellent properties, such as surface hardness, abrasion resistance, etc.

This application is a divisional of copending application Ser. No.902,736, filed on May 3, 1978 now U.S. Pat. No. 4,190,699.

The present invention relates to a coating composition and a method forimprovement of a surfaces hardness of various products by applying thesame. More particularly, it relates to a coating composition useful forimproving the surface properties, such as surface hardness and chemicalresistance, of plastics products, wooden products, metallic products, orthe like, and to a method for improvement of a surface hardness of theseproducts by applying the coating composition to the surface of the baseproducts such as plastics products, wooden products, metallic products,or coated products thereof, preferably after forming an under coatinglayer having an excellent adhesion, and further to a formed articlehaving an excellent abrasion resistance which is produced by applying anunder coat onto the surface of a base product, baking the under coatedproduct, applying the coating composition thereto, and then baking theresultant.

Plastics, for example plastics such as polycarbonate, polymethylmethacrylate, polystyrene and polyvinyl chlorine, are useful for manyapplications because of their light weight, easy processability and highimpact resistance. However, these materials are inferior in abrasionresistance and solvent resistance and the surface thereof are readilyinjured by rubbing and furthermore are easily swollen or dissolved bysolvent contact.

In order to eliminate these defects, it is proposed to coat the surfaceof the plastics with various thermosetting resins, such as melamineresin, thermosetting acrylic resin, polyester resin, polyurethane resin,or silicone resin. However, even by using these resins, it is difficultto obtain the desired product being satisfactory in all properties, suchas surface hardness, abrasion resistance, hot water resistance,weatherability, or the like. When the hardness of the coating film isincreased, it occasionally results in loss of flexibility and crack ofthe film by the test for the hot water resistance. On the other hand,when the flexibility of the film is increased, it results in lowering ofthe hardness of the coating film. Besides, the coating film is inferiorin an adhesion to plastics such as polycarbonate or metals such asaluminum.

The present inventors have intensively studied to find an improvedcoating composition which can give a coating film having both excellenthardness and excellent flexibility without deteriorating otherproperties, such as hot water resistance and weatherability. As theresult, it has been found that the desired coating composition can beobtained by incorporating specific silicon-containing compounds andspecific organic compounds, and further that when a base material iscoated with the coating composition and followed by baking thereof, theproduct is improved in its abrasion resistance, and further, when anunder coat layer is formed between the layer of the coating compositionand the base material, the adhesion of the coating layer to the basematerial is improved, and thereby, the properties, such as abrasionresistance, adhesion and solvent resistance, of the product areimproved.

An object of the present invention is to provide an improved coatingcomposition useful for improving the surface properties such as surfacehardness and chemical resistance of various products, such as plasticsproducts, wooden products, or metallic products.

Another object of the invention is to provide a method for improvementof a surface hardness of these products.

A further object of the invention is to provide a coated article havingan excellent abrasion resistance.

Other objects of the invention will be apparent from the followingdescription.

The coating composition of the present invention comprises:

(A) 100 parts by weight of partially hydrolyzed silicon compoundsconsisting essentially of co-partial hydrolyzates of a tetraalkoxysilaneof the formula: Si(OR¹)₄ wherein R¹ is an alkyl having 1 to 4 carbonatoms and an organic silicon compound of the formula: R_(n) ²Si(OR³)_(4-n) wherein n is an integer of from 1 to 3, R² is ahydrocarbon group having 1 to 6 carbon atoms and R³ is an alkyl having 1to 4 carbon atoms and/or a mixture of partial hydrolyzates of eachtetraalkoxysilane and organic compound, said partially hydrolyzedsilicon compounds containing said partially hydrolyzed tetraalkoxysilane(calculated as SiO₂) and said partially hydrolyzed organic siliconcompound (calculated as R_(n) ² SiO_(m) wherein m=(4-n)/2) in the ratioof 5/95 to 95/5 by weight, and the weight (100 parts by weight) of saidpartially hydrolyzed silicon compounds being also calculated as SiO₂ forsaid partially hydrolyzed tetraalkoxysilane and as R_(n) ² SiO_(m) forsaid partially hydrolyzed organic silicon compound,

(B) 10 to 400 parts by weight of at least one member selected from acopolymer of an alkyl acrylate and/or an alkyl methacrylate(hereinafter, referred to as "alkyl (meth)acrylate") and a hydroxyalkylacryate and/or a hydroxyalkyl methacrylate (hereinafter, referred to as"hydroxyalkyl (meth)acrylate"), which copolymer is, hereinafter,referred to as "acrylic copolymer-I"; a copolymer of at least one of anN,N-dialkylaminoalkyl acrylate and an N,N-dialkylaminoalkyl methacrylate(hereinafter, referred to as "N,N-dialkylaminoalkyl (meth)acrylate") andan N,N-dialkylacrylamide and an N,N-dialkylmethacrylamide (hereinafter,referred to as "N,N-dialkyl(meth)acrylamide") and at least one of ahydroxyalkyl (meth)acrylate and an alkyl (meth)acrylate, which copolymeris, hereinafter, referred to as "acrylic copolymer-II"; and a monomer oroligomer having two or more hydroxy groups (hereinafter, referred to as"polyol"), and

(C) 0 to 300 parts by weight of an etherified methylomelamine, providedthat when the component (B) is the polyol, said etherifiedmethylolmelamine is contained in an amount of 0.5 to 1.5 gram equivalentper 1 gram equivalent of the polyol within 300 parts by weight, whereinthese components (A), (B) and (C) are dissolved in a solvent. Thiscoating composition may occasionally be referred to as "top coatingcomposition", or "silicic coating composition".

The coating composition is applied to the surface of various products,such as plastics products, wooden products, metallic products, or thelike, and thereby, an excellent surface hardness is given thereto.

When the coating composition is applied, an under coat layer maypreviously be formed onto the products. A composition useful for theunder coat comprises:

(1) a polymer (I) having a repeating structural unit of the formula:##STR1## wherein R⁴ and R⁵ are each hydrogen, a lower alkyl having 1 to5 carbon atoms, or carboxyl group, and X is a side chain containingcarboxyl or amino group, or

(2) a polymer (II) having a repeating structural unit of the formula:##STR2## wherein R⁶ and R⁷ are each hydrogen, a lower alkyl having 1 to5 carbon atoms or carboxyl group, and Y is a side chain containinghydroxy group, and a repeating structural unit of the formula: ##STR3##wherein R⁸ and R⁹ are each hydrogen, a lower alkyl having 1 to 5 carbonatoms, or carboxyl group, and Z is a side chain containing carboxyl,amino, a substituted amino, epoxy or tetrahydrofuryl group.

When the under coating composition and subsequent top coatingcomposition are applied and then baked, there is obtained a coatedproduct having an improved abrasion resistance and an improved adhesionwith the base material.

Suitable examples of the tetraalkoxysilane contained in the component(A) of the present top coating composition are the compounds of theformula: Si(OR¹)₄ wherein the alkoxy group: --OR¹ is methoxy, ethoxy,propoxy or butoxy. Suitable examples of the organic silicon compoundcontained in the component (A) are the compounds of the formula: R_(n) ²Si(OR³)_(4-n) wherein the hydrocarbon group: R² is methyl, ethyl, propylbutyl, pentyl, hexyl, vinyl, allyl or phenyl, and the alkyl group: R³ ismethyl, ethyl, propyl or butyl.

The co-partial hydrolyzates or each partial hydrolyzate of thetetraalkoxysilane and the organic silicon compound may be obtained byhydrolyzing them either separately or together in a solvent, such as amixed solvent of water and an alcohol, in the presence of an acid (e.g.hydrochloric, phosphoric and sulfuric acid, oxalic and maleic acid,acetic and formic acid). Alternatively, the partially hydrolyzed siliconcompounds may be produced by hydrolyzing directly a silicon chloride ormixed chloride (e.g. SiCl₄ or R_(n) SiCl_(4-n)). Generally speaking, itis more preferable to cohydrolyze the mixture of the silicon compoundsrather than hydrolyzing separately each of the silicon compounds andmixing the resultants. The partial hydrolyzed silicon compounds thusobtained contain the partial hydrolyzate of the tetraalkoxysilane(calculated as SiO₂) and the partial hydrolyzate of the organic siliconcompound (calculated as R_(n) ² SiO_(m) wherein m is (4-n)/2) in theratio of 5/95 to 95/5 by weight, preferably 30/70 to 80/20 by weight.When the partial hydrolyzate of the tetraalkoxysilane is contained in anamount of less than 5% by weight, the coating film formed from thecoating composition has a lower hardness and loses abrasion resistancewhich can not be practically used, and on the other hand, when theamount is over 95% by weight, the coating film has a lower flexibilityand cracks tend to occur.

The acrylic copolymer-I used as the component (B) in the present coatingcomposition may be obtained by subjecting an alkyl (meth)acrylate and ahydroxyalkyl (meth)acrylate to a bulk polymerization, emulsionpolymerization, suspension polymerization or solution polymerization inthe presence of a radical polymerization initiator, such asazobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, or thelike. Alkyl (meth)acrylate includes esters of (meth)acrylic acid with analcohol having from 1 to 18 carbon atoms, for example, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, lauryl(meth)acrylate, or the like. Hydroxyalkyl (meth)acrylate includes, forexample, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate,hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, or the like.The ratio of the total weight of at least one alkyl (meth)acrylate andthe total weight of at least one hydroxyalkyl (meth)acrylate, which arecontained in the acrylic copolymer-I, is not critical, but from thestandpoint of the adhesion between the coating film and the undercoating layer and the flexibility of the coating film, the ratio thereofmay preferably be in the range of 10/90 to 90/10 by weight.

The acrylic copolymer-II may be obtained by subjecting one or more of anN,N-dialkylaminoalkyl (meth)acrylate and an N,N-dialkyl(meth)acrylamideand one or more of a hydroxyalkyl (meth)acrylate and an alkyl(meth)acrylate to a bulk polymerization, emulsion polymerization,suspension polymerization or solution polymerization in the presence ofa radical polymerization initiator, such as azobisisobutyronitrile,benzoyl peroxide, di-tert-butyl peroxide, or the like.

The N,N-dialkylaminoalkyl (meth)acrylate includes2-N,N-dimethylamino)ethyl (meth)acrylate, 2-(N,N-diethylamino)ethyl(meth)acrylate, 3-(N,N-diethylamino)propyl (meth)acrylate, or the like.

The N,N-dialkyl(meth)acrylamide includes N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, or the like.

The hydroxyalkyl (meth)acrylate includes 2-hydroxyethyl (meth)acrylate,hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, glycerolmono(meth)acrylate, polyethyleneglycol mono(meth)acrylate, or the like.

The alkyl (meth)acrylate includes methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, or the like.

The ratio of the total weight of one or more of theN,N-dialkylaminoalkyl (meth)acrylate and N,N-dialkyl(meth)acrylamide andthe total weight of one or more of the hydroxyalkyl (meth)acrylate andalkyl (meth)acrylate, which are contained in the acrylic copolymer-II,is not critical, but from the standpoint of the adhesion between thecoating film and the under coating layer and the flexibility of thecoating film, the ratio thereof may preferably be in the range of 95/5to 10/90.

Polyols used in the present invention include ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol, 1,3-propanediol, (1,3-, 1,4- or 2,3-)butanediol, 1,6-hexanediol,1,8-octanediol, 1,10-decanediol, neopentyl glycol, pentaerythritol,glycerin, sorbitol, and polyethylene glycol, polypropylene glycol andethylene glycol-propylene glycol copolymer which have a molecular weightof less than 500. When a polyol having a molecular weight of 500 or moreis used, the coating film tends to show a lower surface hardness andabrasion resistance, while the flexibility thereof is increased.

One or more members selected from the above acrylic copolymer-I, acryliccopolymer-II and polyol are incorporated together with the siliconcomponent into the present top coating composition.

In the top coating composition, the total amount of the component (B)consisting essentially of one or more members selected from the acryliccopolymer-I, acrylic copolymer-II and polyol is in the range of 10 to400 parts by weight, preferably 20 to 250 parts by weight, per 100 partsby weight of the component (A) wherein the weight of the partiallyhydrolyzed tetraalkoxysilane is calculated as SiO₂ and the weight of thepartially hydrolyzed organic silicon compound is calculated as R_(n) ²SiO_(m). When the amount of the component (B) is smaller than 10 partsby weight, the coating film obtained therefrom has an inferior adhesionand also a lower flexibility which results in the occurrence of cracks,and on the other hand, when the amount of the component (B) is over 400parts by weight, the coating film has an inferior hardness.

In order to give both excellent hardness and excellent flexibility tothe coating film, it is preferable to use an etherified methylolmelamine[the component (C)] in addition to the acrylic copolymer-I, acryliccopolymer-II and polyol.

The etherified methylolmelamine includes any known compounds which aredisclosed in many literatures and some of them are commerciallyavailable. Suitable examples of the etherified methylolmelamine arehexamethylolmelamine, pentamethylolmelamine, tetramethylolmelamine, apart or whole of the methylol groups of which may be methylated,ethylated, propylated or butylated. Particularly suitable examples are ahexa(alkoxymethyl)melamine, such as hexa(methoxymethyl)melamine,hexa(ethoxymethyl)melamine, hexa(propoxymethyl)melamine,hexa(isopropoxymethyl)melamine, hexa(butoxymethyl)melamine, orhexa(cyclohexyloxymethyl)melamine.

These etherified methylolmelamines are used alone or in a combination oftwo or more thereof in an amount of 0 to 300 parts by weight per 100parts by weight of the component (A) (calculated as SiO₂ and R_(n) ²SiO_(m)). When the amount of the etherified methylolmelamine is over 300parts by weight, the coating film has an inferior hardness and a loweradhesion after being dipped in hot water and subjected to a test ofweatherability. When the polyol is used as the component (B), it isessential to use the etherified methylolmelamine. When the polyol isused in an amount in excess to that of the etherified methylolmelamine,the unreacted polyol remains in the coating film, which results in alower hardness and durability of the coating film, and on the otherhand, when the amount of the polyol is too small, the coating film losesthe flexibility and cracks tend to occur.

The etherified methylolmelamine is mixed with the polyol in the ratio of1:0.5-1.5 by gram equivalent, preferably 1:0.8-1.2 by gram equivalent(etherified methylolmelamine:polyol). In order to give both hardness andflexibility to the coating film and to regulate the viscosity of thecoating liquid, it is more preferable to previously pre-condensate theetherified methylolmelamine and the polyol and then add the resultingpre-condensate to the component (A), rather than to add them to thecomponent (A) separately.

The present inventors have also found that the amount of the partialhydrolyzate of tetraalkoxysilane contained in the coating compositionused for top coating is largely effective for the hardness of the topcoating film. When the amount of the partial hydrolyzate oftetraalkoxysilane is larger, the coating film has a large hardness andan improved abrasion resistance, but has an inferior flexibility andcracks tend to occur. When the amount of the partial hydrolyzate oftetraalkoxysilane is small the coating film has a small hardness and aninferior abrasion resistance. When the polyol is used as the component(B), the amount of the partial hydrolyzate of tetraalkoxysilane(calculated as SiO₂) is preferably in the range of 6 to 45% by weightbased upon the total weight of the solid components in the top coatingcomposition.

The solvent used in the preparation of the top coating compositionincludes alcohols, ketones, esters, ethers, cellosolves, halogenatedcompounds, carboxylic acids, aromatic compounds, or the like, which maybe used alone or in a combination of two or more thereof. Particularlysuitable examples of the solvent are lower alcohols (e.g. methanol,ethanol, propanol or butanol), cellosolves (e.g. methyl cellosolve,ethyl cellosolve or butyl cellosolve), lower aliphatic carboxylic acids(e.g. formic acid, acetic acid or propionic acid), aromatic compounds(e.g. toluene or xylene), esters (e.g. ethyl acetate or butyl acetate),or the like, which may be used alone or as a mixed solvent. The solventis used so that the solids content of the coating composition achieves aconcentration of 5 to 50% by weight.

The top coating composition is applied to the base material, to which anunder coating composition as mentioned hereinafter is previously appliedand followed by baking. After top coating, the resultant is heated at atemperature higher than 70° C. but lower than the heat deformationtemperature of the base material (in case of a polycarbonate resin, theheat deformation temperature being in the range of 120° to 160° C.) for10 to 200 minutes and thereby the coating composition is cured to give acoating film having excellent hardness and adhesion. In order to lowerthe curing temperature or to shorten the curing time, it is preferableto use a curing accelerator, such as acids (e.g. hydrochloric acid,phosphoric acid or toluenesulfonic acid), ammonium salts (e.g. ammoniumchloride, ammonium nitrate or ammonium thiocyanate), organic amines,metal salts of organic carboxylic acids, metal salts of thiocyanic acid,metal salts of nitrous acids, metal salts of boric acid, organic tincompounds, or the like. Optionally, a commercially availableflow-controlling agent, such as an alkylene oxide-dimethylsiloxane blockcopolymer (e.g. NUC Silicone Y7006, a trade name of Nippon Unicar Co.)may also be used. The curing accelerator and flow-controlling agent maybe used in a small amount, and usually, the curing accelerator may beused in an amount of 0.1 to 5% by weight based on the weight of solidcomponents in the coating composition and the flow-controlling agent maybe used in an amount of 0.01 to 0.1% by weight based on the total weightof the coating composition.

The top coating is carried out by a conventional coating method, such asdipping, spray coating, roller coating or flow coating, and aftercoating, the resultant is cured by heating at 70° C. or higher to give acoating film having excellent hardness, flexibility and chemicalresistance. The thickness of the top coating layer (after curing) ispreferably in the range of 3 to 50 microns, more preferably 5 to 20microns.

In order to increase the adhesion between the top coating layer and thebase material, it is preferable to previously apply an under coatingcomposition to the base material.

The under coating composition comprises the polymer (I) or the polymer(II) as mentioned hereinbefore. The polymer (I) contains at least 5% bymol, preferably 20 to 100% by mol, of the repeating structural unit ofthe formula (I), and the polymer (II) contains at least 2.5% by mol,preferably 10 to 90% by mol, of each repeating structural unit of theformula (II) and the formula (III).

The copolymer (I) may be prepared by polymerizing a vinyl monomer (A) asmentioned hereinafter alone or by copolymerizing the vinyl monomer (A)and another monomer which is copolymerizable with the vinyl monomer (A)by a conventional polymerization method.

Suitable examples of the vinyl monomer (A) are acrylic acid, methacrylicacid, crotonic acid, vinylacetic acid, maleic acid, itaconic acid,aminomethyl acrylate, aminomethyl methacrylate, acrylamide,methacrylamide, crotonamide, or the like, which may be used alone or ina mixture of two or more thereof.

The other monomer copolymerizable with the vinyl monomer (A) or thevinyl monomers (B) and (C) as mentioned hereinafter includes anycompound having at least one ethylenically unsaturated bond in themolecule, for example, olefins (e.g. ethylene), diolefins (e.g.butadiene), vinyl compounds (e.g. vinyl chloride, vinylidene chloride oracrylonitrile, acrylic or methacrylic acid esters (e.g. methyl(meth)acrylate, ethyl (meth)acrylate), (meth)acrylamides (e.g.N,N-dimethyl(meth)acrylamide), or the like, which may be used alone orin a combination of two or more thereof.

Suitable example of the polymer (I) is a copolymer comprising 90 to 5%by weight of one or more amino monomers selected from the groupconsisting of an N,N-dialkylaminoalkyl (meth)acrylate and anN,N-dialkyl(meth)acrylamide, 10 to 50% by weight of methyl methacrylateand 0 to 85% by weight of at least one vinyl compound copolymerizablewith these monomers, and this copolymer is particularly useful when thebase material to be coated is a polycarbonate resin article.

Besides, the polymer (II) may be prepared by copolymerizing the vinylmonomer (B) and the vinyl monomer (C) as mentioned hereinafter,optionally together with other monomers copolymerizable with these vinylmonomers (B) and (C) as mentioned hereinbefore by a conventionalpolymerization method.

Suitable examples of the vinyl monomer (B) are allyl alcohol,N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide,N-(2-hydroxyethyl)acrylamide, N,N-dihydroxymethylacrylamide,N,N-di(2-hydroxyethyl)methacrylamide, 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropylmethacrylate, 1,4-butylene glycol monoacrylate, 1,4-butylene glycolmonomethacrylate, glycerol monomethacrylate, hydroxyallyl methacrylate,polyethylene glycol monoacrylate, polypropylene glycol monomethacrylate,hydroxymethylaminomethyl acrylate, hydroxymethylaminomethylmethacrylate, 2-hydroxyethylaminomethyl acrylate,2-(2'-hydroxyethylamino)ethyl methacrylate,N,N-di(hydroxymethyl)aminomethyl acrylate,N,N-di(hydroxymethyl)aminoethyl methacrylate,N,N-di(2-hydroxyethyl)aminomethyl acrylate, or the like, which may beused alone or in a combination of two or more thereof.

Suitable examples of the vinyl monomer (C) are acrylic acid, methacrylicacid, crotonic acid, vinylacetic acid, maleic acid, itaconic acid,acrylamide, methacrylamide, crotonamide, N-methylacrylamide,N-methylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide,N-propylacrylamide, N-butylacrylamide, N-tert-butylmethacrylamide,N,N-dimethylacrylamide, N,N-dimethylmethacrylamide,N,N-diethylacrylamide, N,N-diethylmethacrylamide,N,N-dipropylmethacrylamide, N,N-dibutylacrylamide,N,N-dibutylmethacrylamide, N-butoxymethylacrylamide,N-iso-butoxymethylmethacrylamide, 2-(N-methylamino)ethyl acrylate,2-(diethylamino)ethyl methacrylate, 2-(N,N-dimethylamino)ethyl acrylate,2-(N,N-dimethylamino)ethyl methacrylate, 2-(N,N-diethylamino)ethylacrylate, 2-(N,N-diethylamino)ethyl methacrylate,2-(N,N-dibutylamino)ethyl acrylate, 2-(N,N-dibutylamino)ethylmethacrylate, 3-(N,N-diethylamino)propyl acrylate,3-(N,N-diethylamino)propyl methacrylate, 2-(N,N-dibutylamino)propylacrylate, 2-(N,N-dibutylamino)propyl methacrylate,3-(N,N-dibutylamino)propyl methacrylate, allyl glycidyl ether, glycidylacrylate, glycidyl methacrylate, glycidyl crotonate, tetrahydrofurfurylacrylate, tetrahydrofurfuryl methacrylate, or the like, which may beused alone or in a combination of two or more thereof.

It is not necessarily required to incorporate a crosslinking agent intothe under coating composition. However, when the top coating compositionis applied to the base material coated with the under coatingcomposition, the organic solvent contained in the top coatingcomposition occasionally corrodes the under coat layer, which results inlowering of the adhesion of the coating film to the base material. Inorder to prevent such a corrosion of the under coat with the solvent, itis preferable to incorporate a crosslinking agent into the under coatingcomposition. The crosslinking agent includes an alkyleneglycoldi(meth)acrylate, an alkyl-etherified methylolmelamine, apolyalkyleneglycol di(meth)acrylate, pentaerythritol diacrylate, or thelike. Among them, hexa(methoxymethyl)melamine andhexa(butoxymethyl)melamine are particularly preferable. Thesecrosslinking agents may be used alone or in a combination of two or morethereof. The crosslinking agent may be used in an amount of 0.05 to 0.7equivalent, preferably 0.2 to 0.4 equivalent, per 1 equivalent of thefunctional group contained in the polymer (I) or polymer (II) such ascarboxyl, amino, substituted amino, hydroxy, epoxy or tetrahydrofuryl.

A crosslinking catalyst is used together with the crosslinking agent.Suitable examples of the crosslinking catalyst are hydrochloric acid,ammonium chloride, ammonium nitrate, ammonium thiocyanate, or the like.The crosslinking catalyst may preferably be used in an amount of 0.05 to0.8 gram equivalent per 1 gram equivalent of the crosslinking agent.

The under coating composition is usually diluted with a diluent to aconcentration suitable for application thereof, when used. Examples ofthe diluent are alcohols (e.g. methanol, ethanol), ethers (e.g. methylcellosolve), ketones (e.g. methyl ethyl ketone), esters (e.g. methylacetate, ethyl acetate), or the like, which may be used alone or in theform of a mixed solvent of two or more thereof. Suitable concentrationof the under coating composition after dilution is in the range of 0.1to 10% by weight, preferably 0.5 to 5% by weight, of the content of thepolymer (I) or the polymer (II).

The under coating composition may optionally contain a small amount of aconventional additive, such as a flow-controlling agent.

The under coating composition containing the polymer (I) or the polymer(II) as the main ingredient and optionally a crosslinking agent, acrosslinking catalyst, a diluent and a flow-controlling agent is appliedto the surface of a base material by a conventional coating method, suchas dipping, spray coating, roller coating or flow coating, and theresultant is dried and further optionally cured by heating at atemperature lower than the heat deformation temperature of the basematerial to give an under coating film. The under coating film maypreferably have a thickness of 0.1 to 1 micron. When the top coatingcomposition is applied to the under-coated base material, the functionalgroups such as hydroxyl, carboxyl or amino groups contained in the undercoating film are reacted with the silicon components contained in thetop coating composition, and thereby, the top coating film is stronglyadhered to the base material via the under coating film.

The base material to be coated with the present coating compositionincludes plastic resins (e.g. polycarbonate resin, polymethylmethacrylate resin, polystyrene resin or polyvinyl chloride resin),metallized products which are produced by depositing a metal (e.g.aluminum) onto a resin sheet (e.g. a polymethyl methacrylate sheet),plated products which are produced by plating a metal (e.g. chromium)onto a resin (e.g. ABS resin), metals (e.g. aluminum or iron), coatedproducts of plastics or metals, or the like. Since the components of theunder coating composition and the top coating composition of the presentinvention have an excellent transparency, these compositions areparticularly useful for coating a clear plastic such as a polycarbonatebase material and for finishing the surface of metallized products orplated products in order to give them an excellent abrasion resistance.

Particularly suitable base materials are polycarbonate resins, forexample, bisphenol type polycarbonate (e.g. 4,4'-isopropylidenediphenolpolycarbonate), polycarbonates disclosed in U.S. Pat. No. 3,305,520 andCrystofer and Fox, "Polycarbonates", pages 161-176 (1962), diethyleneglycol bisallylcarbonate, or the like.

The present invention is illustrated by the following Examples, but isnot limited thereto. In the Examples, "%" and "part" mean % by weightand part by weight unless specified otherwise.

EXAMPLES 1 to 11 and Reference Examples 1 to 4

(1) Preparation of a solution of cohydrolyzation products oftetraethoxysilane and methyltriethoxysilane (Component I):

Tetraethoxysilane (66.7 g) and methyltriethoxysilane (33.3 g) weredissolved in isopropyl alcohol (70 g) and 0.05 N hydrochloric acid (30g) was added to the solution, and the mixture was stirred at roomtemperature to effect hydrolysis. After the reaction, the mixture wasmatured at room temperature for 20 hours or more. The resulting solutioncontained a partial hydrolyzate of tetraethoxysilane (9.6%, calculatedas SiO₂) and a partial hydrolyzate of methyltriethoxysilane (6.3%,calculated as CH₃ SiO₁.5) (SiO₂ :CH₃ SiO₁.5 =60:40).

(2) Preparation of a solution of cohydrolyzation products oftetraethoxysilane and methyltriethoxysilane (Component II):

A reactor provided with a reflux condenser was charged with isopropylalcohol (68 g), tetraethoxysilane (38 g) and methyltriethoxysilane (72g). To the mixture was added 0.05 N hydrochloric acid (36 g), and themixture was heated with stirring at a reflux temperature for 5 hours toeffect hydrolysis. After the reaction, the reaction mixture was cooledto room temperature to give a cohydrolyzation solution which contained apartial hydrolyzate of tetraethoxysilane (5.1%, calculated as SiO₂) anda partial hydrolyzate of methyltriethoxysilane (12.6%, calculated as CH₃SiO₁.5) (SiO₂ :CH₃ SiO₁.5 =29:71).

(3) Preparation of a solution of cohydrolyzation products oftetraethoxysilane and dimethyldiethoxysilane (Component III):

Tetraethoxysilane (83.3 g) and dimethyldiethoxysilane (16.7 g) weredissolved in isopropyl alcohol (70 g) and 0.05 N hydrochloric acid (30g) was added to the solution and the mixture was stirred at roomtemperature to effect hydrolysis. After the reaction, the mixture wasmatured at room temperature for 20 hours or more. The resulting solutioncontained a partial hydrolyzate of tetraethoxysilane (12%, calculated asSiO₂) and a partial hydrolyzate of dimethyldiethoxysilane (4.2%,calculated as (CH₃)₂ SiO) (SiO₂ :(CH₃)₂ SiO=74:26).

(4) Preparation of a solution of cohydrolyzation products oftetraethoxysilane, methyltriethoxysilane and trimethylethoxysilane(Component IV):

Tetraethoxysilane (83.3 g), methyltriethoxysilane (14 g) andtrimethylethoxysilane (2.7 g) were dissolved in ethyl alcohol (70 g) and0.05 N hydrochloric acid (30 g) was added to the solution, and themixture was stirred at room temperature to effect hydrolysis. After thereaction, the resulting mixture was matured at room temperature for 20hours or more. The resulting solution contained a partial hydrolyzate oftetraethoxysilane (12%, calculated as SiO₂), a partial hydrolyzate ofmethyltriethoxysilane (2.6%, calculated as CH₃ SiO₁.5) and a partialhydrolyzate, of trimethylethoxysilane (0.9%, calculated as (CH₃)₃SiO₀.5) [SiO₂ :(CH₃ SiO₁.5 +(CH₃)₃ SiO₀.5)=77:23].

(5) Preparation of a solution of cohydrolyzation products oftetraethoxysilane and methyltriethoxysilane (Component V):

Tetraethoxysilane (88 g) and methyltriethoxysilane (16 g) were dissolvedin isopropyl alcohol (60 g) and 0.05 N hydrochloric acid (36 g) wasadded to the solution, and the mixture was stirred at room temperatureto effect hydrolysis. After the reaction, the mixture was matured atroom temperature for 20 hours or more. The resulting solution containeda partial hydrolyzate of tetraethoxysilane (12.8%, calculated as SiO₂)and a partial hydrolyzate of methyltriethoxysilane (3.0%, calculated asCH₃ SiO₁.5) (SiO₂ :CH₃ SiO₁.5 =81:19).

(6) Preparation of acrylic copolymer-I:

(a) Butyl acrylate (40 g), 2-hydroxyethyl methacrylate (10 g) andazobisisobutyronitrile (0.5 g) were dissolved in ethyl alcohol (300 g).The mixture was stirred at 70° C. for 5 hours under nitrogen gas toeffect polymerization. After the reaction was completed, the reactionmixture was poured into petroleum ether and thereby the unreactedmonomer was removed to give Copolymer (a).

(b) Ethyl acrylate (50 g) and 3-hydroxypropyl methacrylate (10 g) werecopolymerized in the same manner as described in the above (a) to giveCopolymer (b).

(7) Preparation of acrylic copolymer-II:

(c) 2-(N,N-Dimethylamino)ethyl methacrylate (4 g), 2-hydroxyethylmethacrylate (2 g), butyl acrylate (14 g) and benzoyl peroxide (0.2 g)were dissolved in ethyl cellosolve (80 g). The mixture was stirred at85° C. for 4 hours and further at 100° C. for 30 minutes under nitrogengas to give a solution of Copolymer (c).

(d) N,N-Dimethylacrylamide (4 g), 2-hydroxyethyl methacrylate (2 g) andbutyl acrylate (14 g) were copolymerized in the same manner as describedin the above (c) to give a solution of Copolymer (d).

(8) Preparation of a solution of each pre-condensate ofhexa(methoxymethyl)melamine and 1,4-butanediol, 1,6-hexanediol,diethylene glycol, triethylene glycol or tetraethylene glycol:

(a) An 85% phosphoric acid (0.2 ml) was added tohexa(methoxymethyl)melamine (78 g) and 1,4-butanediol (54 g) (gramequivalent ratio=1:1), and the mixture was reacted at 130°-140° C. togive a prepolymer having a molecular weight of about 5,000. To thereaction product was added ethyl cellosolve to give Pre-condensateSolution (a) having a solid content of 75%.

(b) Hexa(methoxymethyl)melamine (78 g) and 1,6-hexanediol (71 g) (gramequivalent ratio=1:1) were condensed in the same manner as described inthe above (a) to give Pre-condensate Solution (b) having a solid contentof 96%.

(c) Hexa(methoxymethyl)melamine (65 g) and diethylene glycol (53 g)(gram equivalent ratio=1:1) were reacted likewise to give a prepolymerhaving a molecular weight of about 30,000. To the prepolymer was addedethyl cellosolve to give Pre-condensate Solution (c) having a solidcontent of 96%.

(d) An 85% phosphoric acid (0.2 ml) was added tohexa(methoxymethyl)melamine (260 g) and triethylene glycol (300 g) (gramequivalent ratio=1:1). The mixture was reacted at 130°-140° C. until42.7 g of a distillate were obtained. To the prepolymer thus obtainedwas added ethyl cellosolve to give Pre-condensate Solution (d) having asolid content of 96%.

(e) An 85% phosphoric acid (0.4 ml) was added tohexa(methoxymethyl)melamine (520 g) and tetraethylene glycol (800 g)(gram equivalent ratio=1:1). The mixture was reacted at 130°-140° C.until 86 g of a distillate were obtained. To the prepolymer thusobtained was added ethyl cellosolve to give Pre-condensate Solution (e)having a solid content of 96%.

(9) Preparation of the coating composition:

To the solution of Component I, Component II and Component V were addedhexa(methoxymethyl)melamine and polyol or a pre-condensate thereof, acuring accelerator, a flow-controlling agent, etc. To the mixture wasadded ethyl cellosolve so that the solid content becomes 10 to 40% togive the coating compositions as shown in Table 1.

(10) Coating and tests of the properties of the coated products:

Polycarbonate sheet (thickness: 3 mm) was washed and coated with theabove-obtained coating compositions. The coated products were cured witha hot-air drier at 130° C. for 2 hours. The polycarbonate sheets thuscoated were subjectd to the following tests:

(i) Adhesion:

This was tested by the so-called "cross-cut tape test". That is, thecoating film was cross-cut by making each 11 parallel lines of nickswith a knife in an interval of 1 mm in the horizontal and verticaldirections so that a hundred cells having an area of 1 mm² were formed,and thereon was bonded an adhesive cellophane tape. The cellophane tapewas then peeled off. The adhesion of the coating film was evaluated bythe number of the remaining cells.

(ii) Abrasion resistance:

Steel wool test: the surface was rubbed with #0000 steel wool. Theabrasion resistance was evaluated according to the following scale.

A: No scratch made on the surface even by strong rubbing.

B: A few scratches made by strong rubbing.

C: Scratches made even by weak rubbing.

Taber abrasion test: It was tested in accordance with ASTM D-1044 byusing a Taber abrader (wheel: CS-10F, load: 500 g). The abrasionresistance was evaluated by a haze (%) after rotating the wheel 500times.

(iii) Boiling water resistance:

The surfaces to be tested were immersed in boiling water for 60 minutes,and thereafter, the state of the coating film was observed.

(iv) Flexibility:

A sample (50 mm×100 mm×thickness 0.7 mm) was bent in a bending radius of15 mm at room temperature. The flexibility was evaluated by theoccurrence of cracks.

(v) Heat cycle test:

A sample was kept in turn at -20° C. and at 80° C. for each 2 hours.This was repeated ten times, and thereafter, the state of the coatingfilm was observed.

These test results are shown in Table 2.

                                      TABLE 1                                     __________________________________________________________________________           Component A                                                                   I   II  V                                                                     (Solid                                                                            (Solid                                                                            (Solid                                                                            Components B and C                                                content                                                                           content                                                                           content                                                                           Etherified                                                                             Polyol                                                   15.9%)                                                                            17.7%)                                                                            15.8%)                                                                            methylolmelamine                                                                       (Component B)                                                                             Pre-condensate Solution                      Part by                                                                           Part by                                                                           Part by                                                                           (Component C)    Part by                                                                           (Components B and C)                  Example No.                                                                          weight                                                                            weight                                                                            weight                                                                            Part by weight                                                                         Kind    weight                                                                            Kind                                                                              Part by weight                    __________________________________________________________________________    Ex. 1  100 --  --  21       1,4-Butanediol                                                                        14  --  --                                Ex. 2  100 --  --   9       Glycerin                                                                               4  --  --                                Ex. 3  --  --  100 11       Neopentyl                                                                              9  --  --                                                            glycol                                            Ref. Ex. 1                                                                           100 --  --  35       --      --  --  --                                Ref. Ex. 2                                                                           100 --  --  --       1,4-Butanediol                                                                        35  --  --                                Ex. 4  100 --  --  --       --      --  a   103                               Ex. 5  --  100 --  --       --      --  a   17                                Ex. 6  --  --  100 --       --      --  a   38                                Ref. Ex. 3                                                                           --  --  100 --       --      --  a   1                                 Ex. 7  --  100 --  --       --      --  b   9                                 Ex. 8  --  --  100 --       --      --  b   20                                Ref. Ex. 4                                                                           --  100 --  --       --      --  b   101                               Ex. 9  100 --  --  --       --      --  c   17                                Ex. 10 100 --  --  --       --      --  d   17                                Ex. 11 100 --  --  --       --      --  e   17                                __________________________________________________________________________     [Note]:                                                                       (1) Etherified methylolmelamine is hexa(methoxymethyl)melamine.               (2) The Precondensate Solution (a) has a solid content of 75%, and the        Precondensate Solution(b), (c), (d) and (e) have a solid content of 96%. 

                                      TABLE 2                                     __________________________________________________________________________           Properties                                                                    Appearance  Abrasion resistance                                               after       Steel wool                                                                          Taber test                                                                          Boiling water                                  Example No.                                                                          curing Adhesion                                                                           test  (Haze: %)                                                                           resistance                                                                            Flexibility                                                                         Heat cycle                       __________________________________________________________________________                                                 test                             Ex. 1  Good   100/100                                                                            A     29    Good    Yes   Good                             Ex. 2  "      "    A     18    "       "     "                                Ex. 3  "      "    A     15    "       "     "                                Ref. Ex. 1                                                                           Crack  "    A     22    Increased crack                                                                       No    Increased crack                  Ref. Ex. 2                                                                           "      "    A     30    "       "     "                                Ex. 4  Good   "    B     35    Good    Yes   Good                             Ex. 5  "      "    A     30    "       "     "                                Ex. 6  "      "    A     13    "       "     "                                Ref. Ex. 3                                                                           Crack  "    A      5    Increased crack                                                                       No    Increased crack                  Ex. 7  Good   "    A     28    Good    Yes   Good                             Ex. 8  "      "    A      7    "       "     "                                Ref. Ex. 4                                                                           "      "    C     42    "       "     "                                Ex. 9  "      "    A     20    "       "     "                                Ex. 10 "      "    A     18    "       "     "                                Ex. 11 "      "    B     23    "       "     "                                __________________________________________________________________________

EXAMPLE 12

To a mixture of ethyl cellosolve (320 g), 2-hydroxyethyl methacrylate(36 g) and dimethylaminoethyl methacrylate (44 g) was addedazobisisobutyronitrile (0.4 g), and the mixture was reacted at 90° C. togive a solution of a copolymer of 2-hydroxyethyl methacrylate anddimethylaminoethyl methacrylate.

To the silicon Component I (100 parts) were added the copolymer solutionobtained above (40 parts), Pre-condensate Solution (a) (10 pars), acuring accelerator and a flow-controlling agent to give a coatingcomposition. The coating composition thus obtained was applied to apreviously washed polycarbonate sheet (thickness: 3 mm). The coatedproduct was cured with a hot-air drier at 130° C. for 2 hours. Thecoating film thus prepared showed steel wool test: A, and excellentboiling water resistance and flexibility.

In the following Examples 13 to 35 and Reference Examples 5 to 11, theComponents I to V, Copolymers (a) to (d) and Pre-condensate Solutions(a) to (e) as prepared in the above Examples 1 to 11 were used. Besides,the under coating compositions were prepared as follows:

(a) 2-Hydroxyethyl methacrylate (76 g), dimethylaminoethyl methacrylate(4 g) and azobisisobutyronitrile (0.4 g) were dissolved in ethylcellosolve (320 g), and the mixture was stirred at 90° C. for 4 hoursunder nitrogen gas to effect copolymerization. To the resulting solution(100 g) were added hexa(methoxymethyl)melamine (2.8 g), ammoniumchloride (0.18 g), ethyl cellosolve (900 g) and a small amount of aflow-controlling agent to give Under Coating Composition (a).

(b) 2-Hydroxyethyl methacrylate (36 g), dimethylaminoethyl methacrylate(14 g), methyl methacrylate (50 g) and azobisisobutyronitrile (0.4 g)were dissolved in ethyl cellosolve (320 g), and the mixture was stirredat 90° C. for 4 hours under nitrogen gas to effect copolymerization. Tothe resulting solution (100 g) were added hexa(methoxymethyl)melamine(1.3 g), ammonium chloride (0.18 g), ethyl cellosolve (900 g) and asmall amount of a flow-controlling agent to give Under CoatingComposition (b).

EXAMPLES 13 to 17 and Reference Examples 5 to 8

A previously washed polycarbonate sheet was coated with the above UnderCoating Composition (a) except Reference Example 8. The coated productswere cured with a hot-air drier at 130° C. for 10 minutes to give undercoating films having a thickness of about 0.5 micron.

A solution of Component I, Component II, Component III or Component IV,Copolymer (a) or Copolymer (b), and optionallyhexa(butoxymethyl)melamine, a curing accelerator and a flow-controllingagent were mixed in the ratio as shown in Table 3. The mixtures weredissolved in a mixture of n-butanol (60 parts), acetic acid (40 parts)and xylene (20 parts) to give coating compositions.

The coating compositions obtained above were applied to under-coatedpolycarbonate sheets, except Reference Example 8, and the resultingproducts were cured with a hot-air drier at 130° C. for 2 hours to givetop coating films having a thickness of about 10 micron. The coatingfilms thus obtained were subjected to various tests, and the propertiesof the coating films are shown in Table 4. In these tests, adhesion andabrasion resistance were tested in the same manner as described inExamples 1 to 11. The boiling water resistance was tested by immersingthe surfaces to be tested in hot water at 80° C. for 2 hours andthereafter observing the state of the coating film. The heat cycle testwas carried out by immersing in turn a sample into boiling water at 80°C. for 10 seconds and ice-salt water at -° C. for 10 seconds (this beingrepeated ten times) and then observing the state of the coating film.

In these examples and reference examples, bisphenol type polycarbonatesheet and diethylene glycol bisallylcarbonate sheet were used as thepolycarbonate sheet. In both sheets, the same results were obtained.

                                      TABLE 3                                     __________________________________________________________________________                                       Component (C)                                              Component (A)                                                                         Component (B)                                                                            [Hexa(butoxymethyl-                                        (100 parts by                                                                         (Acrylic copolymer-I)                                                                    melamine]                                  Example No.                                                                           Under coating                                                                         weight) Kind                                                                             Part by weight                                                                        Part by weight                                                                           Additives                       __________________________________________________________________________    Ex. 13  Yes     I       a   4      2          U                               Ex. 14  "       II      a  10      10         --                              Ex. 15  "       III     a   6      --         V                               Ref. Ex. 5                                                                            "       I       -- --      --         U                               Ref. Ex. 6                                                                            "       III     -- --      --         V                               Ex. 16  "       IV      a  20      --         W                               Ex. 17  "       IV      b  15      5          "                               Ref. Ex. 7                                                                            "       IV      -- --      --         "                               Ref. Ex. 8                                                                            No      IV      -- --      --         "                               __________________________________________________________________________     [Note]:                                                                       U: Sodium acetate (0.4 part)                                                  V: Potassium thiocyanate (0.4 part) and NUC Silicone Y7006 (a surfactant      sold by Nippon Unicar Co.) (0.2 part)                                         W: Sodium acetate (0.4 part) and NUC Silicone Y7006 (0.2 part)           

                                      TABLE 4                                     __________________________________________________________________________            Appearance  Abrasion                                                                           Boiling water                                        Example No.                                                                           after curing                                                                         Adhesion                                                                           resistance                                                                         resistance                                                                            Heat cycle test                              __________________________________________________________________________    Ex. 13  Good   100/100                                                                            A    Good    Good                                         Ex. 14  "      "    B    "       "                                            Ex. 15  "      "    A    "       "                                            Ref. Ex. 5                                                                            Slight crack                                                                         "    A    Increased crack                                                                       Increased crack                              Ref. Ex. 6                                                                            Good   "    A    Good    Crack                                        Ex. 16  "      "    A    "       Good                                         Ex. 17  "      "    A    "       "                                            Ref. Ex. 7                                                                            Slight crack                                                                         "    A    Increased crack                                                                       Increased crack                              Ref. Ex. 8                                                                            Good    0/100                                                                             *    Peeled off                                                                            Peeled off                                   __________________________________________________________________________     [Note]:                                                                       Owing to the inferior adhesion, the coating film was peeled off by rubbin     with the steel wool.                                                     

EXAMPLES 18 to 21 and Reference Example 9

A solution of Component I, Copolymer (c) or Copolymer (d), andoptionally methylated methylolmelamine and a curing accelerator (sodiumacetate, 0.4 part) were mixed in the ratio as shown in Table 5. Themixture is dissolved in a mixture of isopropanol (20 parts), acetic acid(10 parts) and ethyl cellosolve (20 parts) to give coating compositions.

The coating compositions were applied to polycarbonate sheets which werepreviously washed and coated with Under Coating Composition (a) as inExamples 13-17. The coated products were cured with a hot-air drier at130° C. for one hour. The coating films thus produced were subjected tovarious tests, and the properties of the coating films are shown inTable 5. In the tests, the boiling water resistance was tested byimmersing the surfaces to be tested in boiling water at 60° C. for 30minutes and thereafter observing the state of the coating film, and theother tests were done in the same manner as described in Examples 1 to11.

In these examples and reference examples, bisphenol type polycarbonatesheet and diethylene glycol bisallylcarbonate sheet were used as thepolycarbonate sheet. In both sheets, the same results were obtained.

                                      TABLE 5                                     __________________________________________________________________________           Component A                                                                           Component B                                                           (Solid con-                                                                           (Copolymer                                                            tent 15.9%)                                                                           solution)                                                                             Melamine**                                                                          Before boiling water resistance                                                                After boiling water                                                           resistance test                 Example                                                                              Part by     Part by                                                                           Part by           Abrasion         Abrasion            No.    weight  Kind*                                                                             weight                                                                            weight                                                                              Appearance                                                                           Adhesion                                                                           resistance                                                                         Appearance                                                                           Adhesion                                                                           resistance          __________________________________________________________________________    Ex. 18 100     c   50  --    Good   100/100                                                                            A    Good   100/100                                                                            A                   Ex. 19 "       c   10  --    "      "    A    "      "    A                   Ref. Ex. 9                                                                           "       --  --  --    Crack   0/100                                                                             A    Increased                                                                             0/100                                                                             A                                                                 crack                           Ex. 20 "       d   50  --    Good   100/100                                                                            A    Good   100/100                                                                            A                   Ex. 21 "       c   50  15    "      "    A    "      "    A                   __________________________________________________________________________     [Note]:                                                                       *The copolymer (c) and (d) have both a solid content of 20%.                  **The melamine is a 70% solution of a methylated methylolmelamine in ethy     cellosolve (Sumimal M 55, a trade name of Sumitomo Chemical Company,          Limited).                                                                

EXAMPLES 22 to 35 and Reference Examples 10 to 11

A solution of Component I, Component II or Component V,hexa(methoxymethyl)melamine [Component (C)], a polyol [Component (B)] orits Pre-condensate Solution (a) to (e) and a curing accelerator weremixed in the ratio as shown in Table 6. To the mixture was added ethylcellosolve so that the solid content thereof became 10 to 40% to givecoating compositions.

The coating compositions were applied to polycarbonate sheets which werepreviously washed and coated with Under Coating Composition (a) or (b),except Examples 27 and 31. The coated products were cured with a hot-airdrier at 130° C. for 2 hours. The properties of the coating films thusprepared were tested in the same manner as described in Examples 1 to11, and the results are shown in Table 7.

In these examples and reference examples, bisphenol type polycarbonatesheet and diethylene glycol bisallylcarbonate sheet were used as thepolycarbonate sheet. In both sheets, the same results were obtained.

                                      TABLE 6                                     __________________________________________________________________________                           Components (B) and (C) (Pre-condensate)                               Component A             [Hexa(methoxy-                                        (100 parts by           methyl)-melamine]                      Example No.                                                                          Under coating                                                                         weight) Kind    Part by weight                                                                        (Part by weight)                                                                         Additives                   __________________________________________________________________________    Ex. 22 a       I       1,4-Butanediol                                                                        14      21         P                           Ex. 23 a       I       Glycerin                                                                              4        9         P                           Ex. 24 a       V       Neopentyl                                                                             9       11         Q                                                  glycol                                                 Ref. Ex. 10                                                                          a       I       --      --      35         P                           Ex. 25 a       I       1,4-Butanediol                                                                        55      --         P                           Ex. 26 a       I       a       103     --         P                           Ex. 27 --      I       a       103     --         P                           Ex. 28 b       II      a       17      --         P                           Ex. 29 a       V       a       38      --         R                           Ref. Ex. 11                                                                          b       V       a       1       --         P                           Ex. 30 a       V       b       20      --         P                           Ex. 31 --      V       b       20      --         P                           Ex. 32 b       I       b       105     --         P                           Ex. 33 a       I       c       17      --         R                           Ex. 34 a       I       d       17      --         R                           Ex. 35 a       I       e       17      --         R                           __________________________________________________________________________     [Note]:                                                                       P: Ammonium thiocyanate (0.7 part)                                            Q: Ptoluenesulfonic acid (0.2 part)                                           R: Ammonium nitrate (0.5 part)                                           

                                      TABLE 7                                     __________________________________________________________________________           Before boiling water resistance                                                           Abrasion resistance                                                                       After boiling water resistance test                               Steel wool                                                                          Taber test**      Abrasion                                                                           Flexi-                                                                            Heat cycle                Example No.                                                                          Appearance                                                                           Adhesion                                                                           test  (Haze: %)                                                                           Appearance                                                                           Adhesion                                                                           resistance                                                                         bility                                                                            test                      __________________________________________________________________________    Ex. 22 Good   100/100                                                                            A     29    Good   100/100                                                                            A    Yes Good                      Ex. 23 "      "    A     18    "      "    A    "   "                         Ex. 24 "      "    A     15    "      "    A    "   "                         Ref. Ex. 10                                                                          Crack  "    A     22    Increased                                                                            "    A    No  Increased                                                crack                crack                     Ex. 25 Good   "    B     40    Good   "    B    Yes Good                      Ex. 26 "      "    B     35    "      "    B    "   "                         Ex. 27 "      "    B     35    "       0/100                                                                             *    "   "                         Ex. 28 "      "    A     30    "      100/100                                                                            A    "   "                         Ex. 29 "      "    A     13    "      "    A    "   "                         Ref. Ex. 11                                                                          Crack  "    A      5    Increased                                                                            "    A    No  Increased                                                crack                crack                     Ex. 30 Good   "    A      7    Good   "    A    Yes Good                      Ex. 31 "      "    A      7    "       0/100                                                                             *    "   "                         Ex. 32 "      "    B     42    "      100/100                                                                            B    "   "                         Ex. 33 "      "    A     20    "      "    A    "   "                         Ex. 34 "      "    A     20    "      "    A    "   "                         Ex. 35 "      "    A     23    "      "    A    "   "                         __________________________________________________________________________     [Note]:                                                                       *The coating film had an inferior adhesion, and hence, it was peeled off      by rubbing a steel wool.                                                      **The untreated polycarbonate sheet had a haze of 45 to 50%.             

EXAMPLE 36

Copolymers or homopolymers were prepared by using a co-monomer ormonomer, a solvent and a polymerization initiator as shown in Table 8.To the copolymers or homopolymers were added a crosslinking agent, acuring accelerator and a solvent as shown in Table 9 to give UnderCoating Compositions (c) to (l).

A previously washed polycarbonate sheet was coated with the UnderCoating Compositions (c) to (l). The coated products were cured with ahot-air drier at 130° C. for 10 minutes. The polycarbonate sheetsunder-coated with Under Coating Compositions (c) to (l) were coated withthe coating composition as prepared in Example 29, and the resultingproducts were likewise cured at 130° C. for 2 hours. The coating filmsshowed an excellent adhesion after the boiling water resistance test.

In this example, bisphenol type polycarbonate sheet and diethyleneglycol bisallylcarbonate sheet were used as the polycarbonate sheet. Inboth sheets, the same results were obtained.

                                      TABLE 8                                     __________________________________________________________________________                                                             Poly-                                                                         merization                                                                    conditions                                                         Polymerization                                                                           Tem-                 Co-monomer or monomer                Solvent  initiator  per-                 Poly-       Weight      Weight   Weight   Weight     weight                                                                            ature                                                                            Time              mer Kind    (g) Kind    (g) Kind (g) Kind (g) Kind   (g) (°C.)                                                                     (hr)              __________________________________________________________________________    c   2-Hydroxyethyl                                                                        36  Dimethyl-                                                                             44  --   --  Ethyl                                                                              320 Azobisiso-                                                                           0.4 90 2                     methacrylate                                                                              aminoethyl           cello-   butyronitrile                                   methacrylate         solve                                    d   2-Hydroxyethyl                                                                        20  Dimethyl-                                                                             20  Methyl                                                                             60  "    "   "      "   "  "                     methacrylate                                                                              aminoethyl  meth-                                                             methacrylate                                                                              acrylate                                          e   2-Hydroxyethyl                                                                        51.5                                                                              Acrylic acid                                                                          28.5                                                                              --   --  "    "   "      "   "  "                     methacrylate                                                              f   2-Hydroxyethyl                                                                        38  Glycidyl metha-                                                                       42  --   --  "    "   "      "   80 4                     methacrylate                                                                              crylate                                                       g   2-Hydroxyethyl                                                                        51.7                                                                              Acrylamide                                                                            28.3                                                                              --   --  Ethyl                                                                              220 "      "   "  6                     methacrylate                     cello-                                                                        solve                                                                         + water                                                                            100                                 h   2-Hydroxyethyl                                                                        45  N-Methylol-                                                                           35  --   --  Ethyl                                                                              320 "      "   "  "                     methacrylate                                                                              acrylamide           cello-                                                                        solve                                    i   2-Hydroxyethyl                                                                        40  Tetrahy-                                                                              52  --   --  "    360 "      0.5 "  2                     methacrylate                                                                              drofurfuryl                                                                   methacrylate                                                  j   Acrylamide                                                                            20  Tetrahy-                                                                              50  --   --  Ethyl                                                                              230 "      0.4 90 "                                 drofurfuryl          cello-                                                   methacrylate         solve                                                                         + water                                                                            100                                 k   "       50  --      --  --   --  Water                                                                              200 Ammonium                                                                             0.5 80 "                                                               persulfate                      l   Acrylic acid                                                                          20  --      --  --   --  "    "   Ammonium                                                                             "   90 "                                                               peroxide                        __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________    Under Copolymer or                                                            coating                                                                             homopolymer                                                                            Crosslinking agent                                                                         Curing accelerator                                                                      Solvent                                 composition                                                                         Kind                                                                             Weight (g)                                                                          Kind   Weight (g)                                                                          Kind                                                                              Weight (g)                                                                          Kind  Weight (g)                        __________________________________________________________________________    c     c  100   Hexa(metoxy-                                                                         1.4   NH.sub.4 Cl                                                                       0.19  Ethyl 900                                              methyl)-               cellosolve                                             melamine                                                       d     d  "     Hexa(metoxy-                                                                         0.7   "   0.10  Ethyl "                                                methyl)-               cellosolve                                             melamine                                                       e     e  "     Hexa(metoxy-                                                                         1.9   "   0.27  Ethyl "                                                methyl)-               cellosolve                                             melamine                                                       f     f  "     Hexa(metoxy-                                                                         1.4   "   0.20  Ethyl "                                                methyl)-               cellosolve                                             melamine                                                       g     g  "     Hexa(metoxy-                                                                         1.9   "   0.27  Ethyl                                                  methyl)-               cellosolve                                                                          675                                              melamine               + water                                                                             225                               h     h  "     Hexa(metoxy-                                                                         1.7   "   0.24  Ethyl 900                                              methyl)-               cellosolve                                             melamine                                                       i     i  "     Hexa(metoxy-                                                                         1.3   "   0.18  Ethyl "                                                methyl)-               cellosolve                                             melamine                                                       j     j  "     Hexa(metoxy-                                                                         1.4   "   0.20  Ethyl                                                  methyl)-               cellosolve                                                                          675                                              melamine               + water                                                                             225                               k     k  "     Hexa(metoxy-                                                                         2.0   "   0.08  Ethyl                                                  methyl)-               cellosolve                                                                          300                                              melamine               + water                                                                             600                               l     l  "     Hexa(metoxy-                                                                         1.0   "   0.05  Ethyl                                                  methyl)-               cellosolve                                                                          150                                              melamine               + water                                                                             300                               __________________________________________________________________________

EXAMPLE 37

An under coating composition and a silicic coating composition wereprepared as follows:

(1) Preparation of an under coating composition:

2-(N,N-Dimethylamino)ethyl methacrylate (7 g), methyl methacrylate (8g), 2-hydroxyethyl methacrylate (5 g) and benzoyl peroxide (0.2 g) weredissolved in ethyl cellosolve (80 g), and the mixture was stirred at 85°C. for 4 hours and further at 100° C. for 30 minutes under nitrogen gasto effect copolymerization. To the resulting solution (10 parts) wasadded ethyl cellosolve (90 parts) to give a copolymer solution for undercoating.

(2) Preparation of a silicic coating composition:

Tetraethoxysilane (66.7 g) and methyltrimethoxysilane (33.3 g) weredissolved in isopropyl alcohol (70 g), and thereto was added 0.05 Nhydrochloric acid (30 g). The mixture was stirred at room temperature toeffect hydrolysis. After the reaction, the resulting mixture was maturedat room temperature for 20 hours or more. To a solution of a partialhydrolyzate of silicon compounds (100 parts) and the copolymer solutionfor under coating (30 parts) obtained above were dissolved a mixture ofn-butanol (80 parts) acetic acid (40 parts) and sodium acetate (0.4part) to give a coating composition.

A polycarbonate sheet (thickness: 2 mm) was washed with a neutraldetergent and then with water and coated with the under coatingcomposition obtained above. The coated product was cured with a hot-airdrier at 130° C. for 30 minutes. The under-coated polycarbonate sheetwas coated with the silicic coating composition obtained above, and theresulting product was cured with a hot-air drier at 130° C. for 2 hours.The thus treated polycarbonate sheet had a clear, smooth surface, whichwas not injured even by strongly scratching with a finger nail and had agood surface hardness (abrasion resistance by the steel wool test: noscratch) and also had a good adhesion (the crosscut tape test: nopeeling off, 100/100).

In this example, bisphenol type polycarbonate sheet and diethyleneglycol bisallylcarbonate sheet were used as the polycarbonate sheet. Inboth sheets, the same results were obtained.

EXAMPLE 38

A silicic coating composition was prepared in the same manner asdescribed in Example 37 except that a copolymer of butyl acrylate and2-hydroxyethyl methacrylate (ratio by weight: 4/1) (6 parts) was usedinstead of the copolymer solution for under coating (30 parts). Apolycarbonate sheet was treated in the same manner as in Example 37. Thethus treated polycarbonate sheet had a clear, smooth surface, a goodadhesion (the cross-cut tape test: 100/100) and a good surface hardness(abrasion resistance by the steel wool test: no scratch).

In this example, bisphenol type polycarbonate sheet and diethyleneglycol bisallylcarbonate sheet were used as the polycarbonate sheet. Inboth sheets, the same results were obtained.

EXAMPLE 39

A polymethyl methacrylate sheet (thickness: 2 mm), one surface of whichwas mirror-finished by depositing aluminum thereon in a vacuum, wascoated with the same under coating composition as used in Example 37.The coated product was cured at 80° C. for 60 minutes. The resultingsheet was further coated with the same silicic coating composition asused in Example 38, and the resulting product was cured at 80° C. for 2hours. The polymethyl methacrylate sheet thus treated had no haze andwas clear in both surfaces, and had a good adhesion (the cross-cut tapetest: 100/100) and a good surface hardness (the steel wool test: noscratch) in both surfaces, and both sides of the sheet act as mirrors.

Reference Example 12

A polymethyl methacrylate sheet was treated in the same manner asdescribed in Example 39 except that the under coating composition wasnot coated. The polymethyl methacrylate sheet thus treated had a goodadhesion (the cross-cut tape test: 100/100) in the surface which was notdeposited with aluminum, but the surface which was deposited had a badadhesion (the cross-cut tape test: 0/100) and had a bad surface hardness(the steel wool test: scratches, wherein the deposited metal was deletedand hence the sheet could be seen through).

EXAMPLE 40

An aluminum sheet (thickness: 1 mm, JIS A 1050 P) was coated with theunder coating composition as used in Example 37, and the coated productwas cured at 140° C. for 30 minutes. The under-coated aluminum sheet wasfurther coated with the silicic coating composition as used in Example38, and the resulting product was cured at 130° C. for 2 hours. Thealuminum sheet thus treated had no haze and a smooth surface and had agood adhesion (the cross-cut tape test: 100/100) and had a good surfacehardness (the steel wool test: no scratch).

What is claimed is:
 1. A coating composition consisting essentiallyof:(A) 100 parts by weight of partially hydrolyzed silicon compoundsconsisting essentially of co-partial hydrolyzates of a tetraalkoxysilaneof the formula (Si(OR¹)₄ wherein R¹ is an alkyl having 1 to 4 carbonatoms and an organic silicon compound of the formula: R_(n) ²Si(OR³)_(4-n) wherein n is an integer of from 1 to 3, R² is ahydrocarbon group having 1 to 6 carbon atoms and R³ is an alkyl having 1to 4 carbon atoms and/or a mixture of partial hydrolyzates of eachtetraalkoxysilane and organic silicon compound, said partiallyhydrolyzed silicon compounds containing said partially hydrolyzedtetraalkoxysilane, calculated as SiO₂, and said organic partiallyhydrolyzed silicon compound, calculated as R_(n) ² SiO_(m) whereinm=(4-n)/2, in the ratio of 5/95 to 95/5 by weight, and the weight (100parts by weight) of said partially hydrolyzed silicon compounds beingalso calculated as SiO₂ for said partially hydrolyzed tetraalkoxysilaneand as R_(n) ² SiO_(m) for said partially hydrolyzed organic siliconcompound, (B) 10 to 400 parts by weight of a monomer or oligomer havingtwo or more hydroxy groups, and (C) 0 to 300 parts by weight of anetherified methylolmelamine, wherein said etherified methylolmelamine iscontained in an amount of 0.5 to 1.5 gram equivalent per 1 gramequivalent of the monomer or oligomer, said composition being dissolvedin a solvent.
 2. The coating composition according to claim 1, wherein nin the formula: R_(n) ² Si(OR³)_(4-n) is
 1. 3. The coating compositionaccording to claim 1, wherein the partially hydrolyzed silicon compoundsof component (A) contain said tetraalkoxysilane, calculated as SiO₂, andsaid organic silicon compound, calculated as R_(n) ² SiO_(m), in theratio of 30/70 to 80/20 by weight.
 4. The coating composition accordingto claim 1, wherein the component (B) is used in an amount of 20 to 250parts by weight per 100 parts by weight of the component (A).
 5. Thecoating composition according to claim 1, wherein the monomer oroligomer having two or more hydroxy groups of component (B) is a memberselected from the group consisting of ethylene glycol, diethyleneglycol, triethylene glycol, propylene glycol, dipropylene glycol,1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol,1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, neopentyl glycol,pentaerythritol, glycerin and sorbitol.
 6. The coating compositionaccording to claim 1, wherein the monomer or oligomer having two or morehydroxy groups of component (B) is a member selected from the groupconsisting of polyethylene glycols, polypropylene glycols and ethyleneglycolpropylene glycol copolymers which have a molecular weight of lessthan 500.